Acetic esters including alkyl acetate have been widely employed as solvents and plasticizers. Specifically, ethyl acetate, propyl acetate, butyl acetate, isobutyl acetate, isoamyl acetate and the like with a low molecular weight are frequently used as a solvent for lacquers, paints, warnishes, adhesives, etc.; and such acetates as dioctyl phthalate, dibutyl phthalate, and butyl oleate of a high molecular weight are largely used as a plasticizer.
Acetic esters have generally been prepared by an esterification of acetic acid with an alcohol. However, in such esterification, in order to increase the conversion rate, the desired ester product should be removed from the reaction system as the esterification proceeds because the esterification is reversible.
Method of recovering the desired ester varies, depending on a number of factors; such as the difference in the boiling point of the alcohol and the resulting ester, the formation of an azeotrope between the alcohol and water, which is produced during the esterification, or between the ester and water, and so forth. When the boiling point of the resulting ester is lower than that of the corresponding alcohol, it may be readily removed from the reaction product. However, when the boiling point of the resulting ester is equal to or higher than that of the alcohol, its removal process may become rather complex.
For example, ethyl acetate forms a two-component azeotrope with water, and a three-component azeotrope with ethanol and water (ethyl acetate:ethanol:water=83%: 9%: 8%). Processes for producing ethyl acetate using such properties in a batch or continuous system are disclosed in U.S. Pat. Nos. 1,425,624; 1,425,625; 1,454,462 and 1,454,463 assigned to U.S. Industrial Alcohol Co.
Recently, a reactive distillation process has been developed as an improved process, which comprises introducing a high boiling acidic liquid catalyst at the top of the distillation column, and distilling the resulting reaction mixture while carrying out the reaction on each tray of the column. This process, however, has to deal with the problems associated with the catalyst recovery and the reactor corrosion.